The present invention relates generally to the control rods of a Nordic-type nuclear reactor pressure vessel; and more particularly to the extension or lower portion of replacement control rods that connects the control rod to the control rod drive.
As may be appreciated in the art, Nordic-types of boiling water reactors (BWRs) have unique attributes such as, but not limiting of: characteristics, design features, and dimensions. These attributes tend to vary greatly when compared to non-Nordic type BWRs.
A non-limiting example of a Nordic-type BWR is shown in FIG. 1. A typical BWR includes: a reactor pressure vessel (RPV) 10, a core shroud 30 disposed within the RPV 10, and a nuclear fuel core 35. The core shroud 30 is a cylinder that surrounds the nuclear fuel core 35, which includes a plurality of fuel bundle assemblies 40 disposed within the core shroud 30. A top guide 45 and a core plate 50 supports each of the fuel bundle assemblies 40.
An annular region between the core shroud 30 and the RPV 10 is considered the downcomer annulus 25. Coolant water flows through the downcomer annulus 25 and into the core lower plenum 55. Feedwater enters the RPV 10 via a feedwater inlet 15 and is distributed circumferentially within the RPV 10 by a feedwater sparger 20, which is adjacent a core spray line 105. Then, the water in the core lower plenum 55 flows upward through the nuclear fuel core 35. In particular, water enters the fuel bundle assemblies 40, wherein a boiling boundary layer is established. A mixture of water and steam exits the nuclear fuel core 35 and enters the core upper plenum 60 under the shroud head 65. The steam-water mixture then flows through standpipes 70 on top of the shroud head 65 and enters the steam separators 75, which separate water from steam. The separated water is recirculated to the downcomer annulus 25 and the steam exits the RPV 10 via a nozzle 110 for use in generating electricity and/or in another process.
As illustrated in FIG. 1, a conventional jet pump assembly 85 comprises a pair of inlet mixers 95. Each inlet mixer 95 has an elbow welded thereto, which receives pressurized driving water from a recirculation pump (not illustrated) via an inlet riser 100. Some inlet mixers 95 comprise a set of five nozzles circumferentially distributed at equal angles about an axis of the inlet mixer 95. Here, each nozzle is tapered radially and inwardly at the nozzle outlet. This convergent nozzle energizes the jet pump assembly 85. A secondary inlet opening (not illustrated) is located radially outside of the nozzle exit. Therefore, as jets of water exit the nozzles, water from the downcomer annulus 25 is drawn into the inlet mixer 95 via the secondary inlet opening, where mixing with water from the recirculation pump occurs.
The BWR also includes a coolant recirculation system, which provides the forced convection flow through the nuclear fuel core 35 necessary to attain the required power density. A portion of the water is drawn from the lower end of the downcomer annulus 25 via a recirculation water outlet 80 and forced by the recirculation pump into a plurality of jet pump assemblies 85 via recirculation water inlets 90. The jet pump assemblies 85 are typically circumferentially distributed around the core shroud 30 and provide the required reactor core flow. A typical BWR has between sixteen to twenty-four inlet mixers 95.
FIG. 2 is a schematic illustrating an example of a control rod blade 130 in accordance with an embodiment of the present invention. During the operation of the BWR, a control rod drive system (CRD) 120 maneuvers a control rod blade 130 to obtain an optimum power density. The control rod blade 130 typically is surrounded by a plurality of fuel bundle assemblies 40. As illustrated in FIG. 2, the control rod blade 130 typically has a cross or cruciform traverse cross-section. Here, the fuel bundle assemblies 40 surround the control rod blade 130, which may be positioned in the center of the fuel bundle assemblies 40.
The BWR is typically refueled periodically with an excess of reactivity sufficient to maintain operation throughout an operating cycle. During refueling, the RPV 10 is shutdown and some of the fuel bundle assemblies 40 are replaced. In a Nordic-type BWR the fuel bundle assemblies 40 are of the bottom entry type. The CRD 120 is used to remove the spent control rod blades 130 and to then insert the replacement control rod blades 130.
The CRD 120 connects to the control rod blade 130 in order to maneuver the fuel bundle assemblies 40. The control rod blade 130 may be considered a removable component of the Nordic-type of BWR. Moreover, the CRD 120 may be considered a stationary/fixed component of the Nordic-type of BWR.
Known systems of connecting the control rod blade 130 to the CRD 120 typically comprise multiple components. Some of the known systems use non-welded pin joint(s) to connect the multiple components. Some other known systems weld the multiple components together.
There are a few possible problems with the currently known apparatuses and systems for connecting the control rod blade 130 with the CRD 120. Currently known systems may require multiple repairs to the non-welded pin joint(s) or the welded joint. Currently known systems may also experience repeated structural issues with non-welded pin joints (s) or the welded joint. These apparatuses and systems also require longer time to replace the control rod blade 130 and may also expose operators to longer periods of radioactivity.
Based on the above discussion, operators of Nordic-type of BWRs may desire a new or improved apparatus and system for connecting the control rod blade 130 to the CRD 120. The apparatus and system should not require non-welded pin-joints or welds. The apparatus and system should require fewer parts than currently known systems, and allow for a simplified manufacturing process.